Anion surfactants are mixed with other surfactant or a builder to be used in laundry detergents, kitchen detergents, foaming agents for toothpaste, emulsifiers for medicines and cosmetics, other detergents and the like.
There are conventionally known methods for producing relatively high purity anion surfactant powders and particles, including a method of drying to less than 1% by weight of water concentration with a rotary thin film evaporator (JP-A11-5999) and a method of producing an anion surfactant dry powder with a spray drying tower with simultaneously reducing unreacted alcohols (JP-A61-277661).
JP-A2005-68413 describes a method for drying that uses a smaller drying apparatus and loads a smaller drying load than those of JP-A11-5999 and JP-A61-277661, and can be performed at low temperature to cause little heat deterioration. In this method, a water concentration of an anion surfactant slurry is described to be 20 to 40% by weight, from the viewpoints of reduction in thermal energy load and easiness of handling of a dry slurry.